Control devices for the recirculation of compressed combustion gas from the pressure side of a compressor of a supercharging device back to the intake side of the compressor are generally known as divert-air valve devices. The connection between the pressure side and the intake side of the compressor via a bypass line is necessary for the transition from a high load to the thrust mode of the internal combustion engine, so as to prevent a high delivery of the pressure boost pump against a closed throttle flap and the resulting pumping effect, as well as to prevent an excessive sudden drop in the turbocharger speed entailing thermodynamic problems.
Divert-air valves are often actuated electromagnetically, the valve-closure body of the valve being moved by the electromagnetic force. An example for such an arrangement is described in DE 100 20 041 A1 in which a control unit effects control according to given engine data. The valve has a pressure equalizing opening at the valve-closure body, whereby, given a corresponding design of the effective surfaces, an equilibrium of forces is obtained with respect to pneumatic forces. These valves, however, have a drawback in that, despite the pressure equalization of the valve, a large actuating force is required to actuate the valve-closure member during opening, which is why large solenoids must be used, especially when large cross sections must be controlled. At the same time, limitations exist with respect to the opening times that can be achieved.
In the interest of reducing the required magnetic force, DE 102 51 981 A1 describes providing a pneumatically operated divert-air valve whose pressure space is adapted to be connected with the intake side of the compressor via a solenoid valve. This leads to an opening of the valve. However, the differential pressure responsible therefore drops in the open state so that an inadvertent closing of the valve can occur.
DE 10 2005 028 141 A1 describes a bypass valve for internal combustion engines in which an opening of the valve-closure body is produced by lifting a sealing plate electromagnetically from openings via which a fluidic connection of the control pressure space with the intake side of the compressor can be established. In addition, a constant connection between the control pressure space and the pressure side through a pressure equalization opening in the valve-closure body here exists. However, since the latter has a smaller cross section than the openings to the suction side, a force is generated in the opening direction which causes the valve-closure body to open. In the open state, however, the valve-closure body again contacts the sealing plate so that a pressure equilibrium comes to prevail at the valve-closure body. This may lead to an inadvertent closing of the valve due to a spring force acting in the closing direction. The pressure thereafter builds again so that the valve again opens because of the differential pressure. A control circuit with an opening and closing valve is formed, which leads to increased wear.